If you were a male would you rather have a beautiful, impressive, long tail that attracts a lot of women or would you rather have a shorter, less attractive tail that enables you to escape from predators more easily Living out in the wild among many potential predators, a shorter tail would seem more logical since it would be a more useful trait than a good-looking one. Though the most logical choice, it is not always the case. In many species, traits that would normally be considered awkward or cumbersome are actually favorable. Hard to believe as it may be, these seemingly maladaptive traits can prove to be very useful to certain members of many different species as shown by Darwin's Theory of Sexual Selection.
They enhance the ability of the individual to obtain mates and are therefore very important in the reproductive and evolutionary success of many animals. It is first necessary to understand the basics of Natural Selection before being able to show how Sexual Selection leads to extravagant traits. The main idea behind natural selection is that living organisms change and adapt in order to enhance their ability to survive and reproduce. Those animals that adapt will be more likely to survive and produce more offspring than other animals in the same environment that do not (Boyd and Silk 2000, p. 5), as maintained by Darwin's second postulate. Phenotypes that are favored by Natural Selection include the ability to care for offspring, acquire resources, and avoid predators.
The correlation between Natural Selection and Sexual Selection is the next necessary step to understanding how Sexual Selection accounts for awkward traits. The later of the two can be considered a special category of natural selection. It involves selection for traits only concerned with increasing the probability of mating (Krebs and Davies, 1993, p. 89). It is expressed most strongly in th sex whose access to mates is most limited. In mammalian males, sexual selection tends to have a greater impact on behavior and morphology than does other forms of natural selection.
Due to the combination of females investing more in the care of the offspring and the one-to-one population sex ratio, males are usually the ones in competition for females. Male reproductive success also varies much more than that of the female. It mainly depends on their access to sexually receptive females. It is this rivalry that requires males to develop traits that make them more attractive to females through intersexual selection.
Through intrasexual selection, traits are also developed which enhance their success in male-male competition. Intersexual selection can explain the awkward traits such as the peacock's tail and the frog's loud croak, while intrasexual selection can explain traits such as the red deer's antlers. Those favored by intersexual selection are all traits that in one way or another make the male more attractive to the females, therefore increasing their reproductive success. These outcomes would not usually be favored by natural selection since they are most likely to reduce the ability of the animal to survive or acquire resources. Nonetheless, they still evolve since Sexual Selection is often much stronger than normal Natural Selection (Boyd and Silk 2000, p. 216).
Traits favored by intrasexual selection may or may not be favored by Natural Selection. The red deer use their antlers when they fight with other males, but can also be used in defense against predators. Intersexual selection, in which the females are the ones that chose their mate, has an evolutionary effect. As females become pickier in their choice of mates according to their features and / or qualities, both their genes for focus on detail and the attractive, yet sometimes exaggerated, genes of the males that they choose are passed on to the offspring. These offspring are then pickier and have features that are even more exaggerated, and they pass these traits on to their children in a process known as the runaway process, and so on. Intersexual selection favors three main traits among males; those traits that increase the fitness of their mates, indicate good genes, therefore increasing the fitness of the offspring, and those traits that make them more noticeable to females.
Females will tend to choose to mate with males that have traits that confer direct benefits on them, such as the ability to defend superior territories, protect the offspring, and provision the young better. In some insects, for example, females will only copulate with males that provide a large amount of food during courtship. The ability of the male to bring food during courtship indicates his ability to provide for the young. Another preference that females have in the selection of mates is desirable genes. An example of this is the number of eyespots that a male peacock's tail has.
A large number of spots tend to represent better health. Though the female is only attracted to the tail's appearance, by choosing the male with the most eyespots, the peahen is inadvertently choosing a male with a desirable genotype. Lastly, females may prefer males with distinctive traits, even though they do not increase male fitness directly. Many times these traits are considered burdensome because in most cases they get in the way of survival. A good example is the male frogs call. The frog whose croaks are most readily heard are most likely to get more mates.
If the females can hear a certain frog's calls over all the others, so can predators. This makes them more susceptible to predation. Females are a scarce resource for which males compete. For this reason, many aspects of male courtship can be understood by this competition. It can also help account for the seemingly burdensome traits that evolve in many species through this process of sexual selection.